How green will we be after we've snuffed our thousands of Earth Hour candles?

Obviously, it won't be long before we know the answer to the first question. Given the massive response – tens of thousands of businesses and individuals have signed up here – the GTA is bound to be far darker than usual for a short time this evening.

The long-term impact is far less predictable, but far more important.

What is clear is that Earth Hour has achieved a momentum far beyond what its overwhelmed organizers expected, here and around the world.

From just one city – Sydney, Australia – last year it has mushroomed to more than 300 communities around the globe. Canada has leapt in with enthusiasm, with at least 150 taking part. And Ontario leads the provinces, with about 80.

That total puts Ontario ahead of all of Australia, where Sydney and about 70 other cities and towns are involved. No other nation comes close to that level of participation.

Across Canada, more than 4,000 businesses and organizations, large and small, say they'll support Earth Hour. The 1,030 in Toronto include major buildings like the CN Tower and Air Canada Centre, as well as companies that own most downtown highrises.

Many local firms are taking advantage of the Earth Hour buzz to announce plans for long-term cuts in their resource and energy use.

In the GTA, more than 32,000 people have registered on the Earth Hour website.

Earth Hour has grown so big, so fast, that organizers with the World Wildlife Fund report with considerable awe and joy that they've lost control of the event they devised in 2005 as a way to get climate change on Australia's political agenda.

Plenty of officialdom has become involved, as have global corporate heavyweights like McDonald's, Molson Coors and Wal-Mart.

But the main momentum for Earth Hour has come from individuals and local governments, and the way the event has grown is a testament to the power of Internet sites like Facebook and YouTube and the ability of organizers to learn and adjust on the fly.

Enthusiasm is high in surprising places, including South America and India. On the other hand, the event is likely to have less impact in Europe and the U.S., although major American landmarks, including San Francisco's Golden Gate Bridge and Chicago's two tallest office towers, will go dark.

WWF officials say there's a powerful message in the fact that the usual powerhouse countries aren't leading the way, and that even in wealthy places like Canada it's very much a grassroots phenomenon.

"I'm just beginning to get a sense that this is a way of giving voice to a lot of people who don't normally have a voice," says Andy Ridley, who heads the effort in Sydney.

"There's definitely a sense of urgency about the need to start dealing with climate change. It's coming from lots of different places."

That belief is buttressed by events like this week's parade of thousands of people in Bangkok, led by one of Thailand's biggest pop stars, and messages from people in Indian villages who want to participate even with no local government to organize anything.

In oil-rich Dubai, civic officials initially proclaimed the city "not ready" for Earth Hour, but grassroots support for the event changed their minds. Some of the business community followed. The result: For the first time, the door has inched open to discussion of energy conservation and climate change.

To a certain extent, Earth Hour is simply a large global gathering that people can join to make themselves part of a wider community. It has the added bonus that participants can feel they've done a good deed while they've seen a concert, played glow-in-the-dark soccer at Downsview Park or enjoyed a cozy candlelit dinner or barbecue.

On the surface, some of this seems trivial, even counterproductive. Candles produce more greenhouse gases and toxic pollutants than light bulbs, and barbecues are less efficient than most stoves. Coping with this evening's expected fluctuations might actually lead to a small rise in greenhouse gas emissions from coal-burning power plants.

But the point is that Earth Hour is more about symbolism than immediately effective action. If the focus is only on 60 minutes, the cynics and scoffers will be proved right.

If, on the other hand, the event helps propel people, companies and governments to change, it will be a huge success.

That remains to be seen. Organizers believe, though, that Earth Hour has tapped into genuine concern about climate change and a sense that people want to do something about it – even if they're not certain what that is and aren't willing to disrupt their lives very much.

"It's a signal that people care," says Julia Langer of WWF-Canada. "It's a way to do it that's accessible to everyone."

Turning off the lights for an hour is a very tiny step. And to a large extent, life will return to normal soon after they're back on.

Toronto can expect to repeat Sydney's experience: Electricity consumption in the central business district dropped by about 10 per cent during last year's Earth Hour. But since then it's been higher than ever and, since most of Australia's power comes from coal-fuelled generating stations, greenhouse gas emissions are also up.

On the other hand, Ridley says, some Sydney companies have made "significant moves" to more efficient lighting and other equipment and many "are studying how to move toward a more carbon-constrained economy."

This week, Sydney's mayor, Clover Moore, unveiled her vision of a sustainable city in 2030: Among other features, it would no longer be dominated by cars.

"Her people are saying that Earth Hour has moved the city to a place where you can put that up and not be laughed at," Ridley says.

Others suggest the response to Earth Hour is part of a change in social norms, the start of the same process that has made it unacceptable to smoke in public, drive drunk or refuse to recycle, and that's beginning to cast a shadow over those who travel in gas-guzzling SUVs.

The social judgment shows up when friends ask: "What are you doing for Earth Hour?" says Jay Kassirer, who heads Tools of Change, a social marketing consulting firm in Ottawa.

This week, 70 per cent of respondents to an Angus-Reid online poll said they'd participate. Whether they do or not, that result suggests it's becoming de rigueur to at least appear to be on side.

"People are starting to say, `There are serious things happening that we have to be helping to solve,'" Kassirer says. "It's becoming more of a norm to show you're concerned and being involved this way. I'm seeing it from a much broader group than I expected."

Public support can also influence politicians – a crucial issue since individual and local measures, no matter how aggressive, won't stop climate change. Action is required on a national and global scale.

If Earth Hour is big and dramatic enough, and the effort is sustained, it could send a grassroots message that politicians can't ignore.

That's the aim and uncertainty of Earth Hour, Ridley says. "There are no big promises of a great outcome, but maybe a bit of hope."

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